The present invention relates to a method and a device designed to separate solid particles from a liquid, and in particular, to a sedimentation method and device for purifying waste water.
The removal of particulate matter by sedimentation is widely known and used in the field of water and waste treatment. Large, expensive settling tanks are coventionally used to achieve gravity separation of particles from waste water or other liquids. Such tanks must be sufficiently large to retain an average daily flow of waste water for at least several hours to achieve even minimum clarification.
Recently, shallow depth sedimentation devices, such as tube settlers, have been employed to improve clarification and achieve increased clarifying speed. The tube settlers comprise a plurality of relatively small, interconnected tubes which are placed in the flow path of the waste water, and are sized to insure laminar flow characteristics therethrough. As the waste water flows through the tube settler, the particulate matter therein settles onto the inside surfaces of the tubes and collects thereon to form a sludge. Heretofore, removal of the sludge from the tubes was accomplished by mounting the tubes at a slight incline in the direction of flow, temporarily halting waste water flow through the tubes, and allowing the tubes to drain under gravitational forces. This tube settler configuration requires that the separator be shut down for a period of time to accomplish cleaning of the tubes. Further, as sludge collects in the tubes, flow therethrough is restricted, thereby decreasing clarifying speed. Another known method to accomplish tube cleaning, but with continuous waste water separation, is to mount the tubes at an incline in excess of 45.degree., so that as the sludge builds up on the inner surfaces of the tubes, gravitational forces cause the same to slide downwardly, and continuously evacuate the tubes without interrupting the flow of waste water through the settler. However, the steeply inclined tube settlers require longer tubes to accomplish acceptable clarification, increase the resistence to fluid flow therethrough, and expose the waste water to a continuously evacuating stream of sludge which may become re-suspended in the waste water. Also, in the field of sewage treatment, organic matter which is settled from the fluid tends to be rather sticky, and adheres to the walls of the tube settler, thereby exacerbating the tube cleaning problem.